This invention relates to a process for producing silane, more particularly to a process for producing silane at low cost and high yield by use of silica recovered from geothermal hot water as the silica source.
Recently, the demand for polycrystalline silicon is increasing as the material for solar battery and semiconductor. Such a polycrystalline silicon is produced industrially according to, for example, the pyrolysis method in which monosilane is delivered into a pyrolysis furnace to be brought into contact with the surface of silicon core wire heated by current passage at 800.degree. to 1000.degree. C. to decompose and precipitate monosilane thereon (rod-shaped product) or the fluidized method in which monosilane is delivered into a fluidized-bed reactor filled with silicon particles of predetermined particle sizes to be pyrolyzed therein (powdery product).
Accordingly, in production of polycrystalline silicon, it is necessary to use silane as the starting material.
At present, the following processes for the production of silane are widely known (1) the so-called Siemens process wherein heating reduction treatment is applied to a mixture of silica and a carbon material in an arc furnace to produce metallic silicon, which metallic silicon is then halogenated into, for example, dichlorosilane, which dichlorosilane is subjected to disproportionation to produce silane and (2) the so called Stock process wherein silica is allowed to react with metallic magnesium to form magnesium silicide, which magnesium silicide is then reacted with an ammonium halide in liquid ammonia or an inorganic acid such as hydrochloric acid to produce silane.
The process (1), while having the advantage of producing a high purity silane, involves on the other hand the problem of including a diversity of complicated steps to make the production cost higher. In contrast, the process (2) poses a problem in low yield of silane (about 25%).
Thus, in representative processes for production of silane, the state of the art has not necessarily been satisfactory with respect to production cost and yield.